1. Field of the Invention
The present invention relates to a hydraulic circuit for heavy equipment, which can save energy of the hydraulic circuit by minimizing the discharge flow rate of a hydraulic pump through reduction of revolution of an engine when a working device such as a boom and so on is not driven.
More particularly, the present invention relates to a hydraulic circuit for heavy equipment, which can prevent signal pressure that exceeds a predetermined pressure from being formed in a pilot signal path provided in a switching valve to sense whether the switching valve for controlling hydraulic fluid fed to a working device has been shifted.
2. Description of the Prior Art
Referring to FIG. 1, a conventional hydraulic circuit for heavy equipment includes first to fourth hydraulic pumps P1, P2, P3, and P4 connected to an engine; first switching valves 1, 2, and 3 composed of valves installed in flow paths of the first hydraulic pump P1 and shifted to control hydraulic fluid fed to working devices, such as a boom and so on; second switching valves 4, 5, and 6 composed of valves installed in flow paths of the second hydraulic pump P2 and shifted to control hydraulic fluid fed to working devices, such as an arm and so on; third switching valves 7 and 8 composed of valves installed in flow paths of the third hydraulic pump P3 and shifted to control hydraulic fluid fed to a swing device and so on; a pilot signal path 11 connected to a hydraulic tank T1 through the switching valves 1 to 8 to sense whether the switching valves 1 to 8 are shifted, and receiving pilot signal pressure Pi flowing from the fourth hydraulic pump P4 to the pilot signal path 11 through an inlet port Pi1; a throttling part 10 installed on a side of an inlet port Pi1 so that the signal pressure is formed in the pilot signal path 11; and a pressure switch 9 installed on a side of a signal sensing port Pa branch-connected to the pilot signal path 11, and detecting the signal pressure of the pilot signal path 11 so as to control the speed of an engine.
In the case where an operator shifts the switching valves by operating an operation lever (not illustrated), the pilot signal path 11 is intercepted. A connection flow path between the hydraulic pump and the working device during the shifting of the corresponding switching valve is not separately marked.
As illustrated in FIG. 3, the pilot signal path 11 is alternately formed with signal paths a and b on a valve body 12 of the respective valve, and since the signal paths a and b are intercepted in accordance with the shifting of a spool 13, signal pressure is formed in the pilot signal path 11. Simultaneously, the signal pressure is also formed in the signal sensing port Pa branch-connected to the pilot signal path 11.
Accordingly, in a neutral state of the switching valves 1 to 8 connected to the first to third hydraulic pumps P1, P2, and P3, no signal pressure is formed in the pilot signal path 11. Accordingly, it is judged that the working device is not operated, and thus the engine revolution of the equipment is reduced.
By contrast, in the case of shifting any one of the switching valves 1 to 8, the signal pressure is formed in the pilot signal path 11, and thus the engine revolution can be accelerated by the above-described signal pressure.
Accordingly, in the case where a working device such as a boom and so on is not operated, an auto idle function for minimizing a loss of energy of the hydraulic system through reduction of the engine revolution can be performed.
In the conventional hydraulic circuit for heavy equipment as illustrated in FIGS. 1 to 3, a specified gap due to the assembling tolerance occurs between the valve body 12 and the spool 13 so that the respective spool 13 of the above-described switching valves 1 to 8 is slidably shifted in left or right direction in the valve body 12.
As illustrated in FIGS. 2 and 3, the signal paths a and b, which are coupled to the pilot signal path 11, are arranged between pump paths 14 and 15 formed inside the valve body 12 to keep a high pressure therein. Accordingly, high-pressure hydraulic fluid flows into the signal paths a and b through the gap between the valve body 12 and the spool 13.
In this case, due to foreign substances flowing between the valve body 12 and the spool 13, damage or abrasion of the sliding surface occurs, and this causes the amount of hydraulic pump flowing from the hydraulic pump to the signal paths a and b to be increased.
As described above, in the case where the high-pressure signal pressure is formed in the pilot signal path 11 by the high-pressure hydraulic fluid flowing from the hydraulic pump to the signal paths a and b, the pressure in the pressure switch 9 that is installed on the signal sensing line coupled to the pilot signal path 11 exceeds a predetermined pressure, and this causes the damage of the pressure switch 9.